1. Field of the Invention
This invention relates to a method of recognizing an object.
In addition, this invention relates to an apparatus for recognizing an object which can be mounted on a vehicle. Furthermore, this invention relates to a recording medium storing a computer program for recognizing an object.
2. Description of the Related Art
A known object recognition apparatus for a vehicle emits a forward wave beam such as a light beam or a millimeter wave beam from the body of the vehicle, and enables the forward wave beam to scan a given angular region in front of the body of the vehicle. In the case where an object exists in the given angular region, the forward wave beam encounters the object before being at least partially reflected thereby. A portion of the reflected wave beam returns to the apparatus as an echo wave beam. The apparatus detects and recognizes the object in response to the echo wave beam.
The known object recognition apparatus is used in a warning system for a vehicle which alarms when an obstacle such as a preceding vehicle exists in a given angular region in front of the present vehicle. The known object recognition apparatus is used also in a system for a vehicle which controls the speed of the vehicle to maintain a proper distance between the vehicle and a preceding vehicle.
It is known to use a laser beam as a forward wave beam in an object recognition apparatus for a vehicle. In general, the front end of such an object recognition apparatus has a transparent member through which the forward laser beam travels. A waterdrop encounters the transparent member, changing into a lens-like shape thereon. In some cases, the forward laser beam is scattered when traveling through the lens-like shape of water on the transparent member. The scatter increases the cross-sectional area of the forward laser beam. An increase in the cross-sectional area of the forward laser beam reduces the resolution of detection of an object position and the accuracy of detection of an object size.
In general, a given angular region (a given object detectable area or a given detection area) in front of the body of the vehicle is scanned by the forward laser beam while the angular direction of the forward laser beam is sequentially changed among ones separated at equal unit angles. According to an example, in the absence of a lens-like shape of water from a surface of the transparent member, there occur detected echo beams for 5 successive angular directions of the forward laser beam. On the other hand, in the presence of a lens-like shape of water on the surface of the transparent member, there occur detected echo beams for 10 successive angular directions of the forward laser beam. In this case, a detected width of an object is equal to twice the actual width thereof.
The previously-mentioned scatter sometimes causes the forward laser beam to travel out of the detection area in front of the body of the vehicle. When such a forward laser beam encounters an object outside the detection area and is reflected thereby, an echo beam may return to the object recognition apparatus. On the basis of this echo beam, the apparatus erroneously recognizes the object outside the detection area as an object therein.
A member having a slit is used to narrow and make the cross section of a forward laser beam into an ideal shape. Diffraction at the slit causes an increased intensity of light in a peripheral portion of the beam, so that the shape of the cross section of the beam deviates from the ideal one. Therefore, the theoretical shape of the cross section of the forward laser beam which is used in an object recognition apparatus differs from the actual shape thereof. The difference between the theoretical shape and the actual shape causes a decrease in accuracy of object recognition by the apparatus.
Japanese patent application publication number P2000-180532A discloses a method of detecting an object position which is used in a scanning-type radar for a vehicle. The radar emits a millimeter wave beam. The method in Japanese application P2000-180532A is designed to implement the following process. In the case where there are a plurality of peaks of the power of a reflected beam and a plurality of mountains formed by the plurality of peaks, and where reflection due to a side lobe is included in the power of the reflected beam, a threshold is set to remove the power of the reflection due to the side lobe so that an angle at a width-wise center in angles defined by peaks of both ends among the remaining peaks is detected as a center position of an object.
U.S. Pat. No. 5,627,511 (corresponding to Japanese patent application publication number 8-122437) discloses a distance measuring apparatus for an automotive vehicle that compensates for the influence of particles floating in the air.
The apparatus of U.S. Pat. No. 5,627,511 outputs laser pulse signals at given angular intervals over an object detectable zone, and receives a signal produced by reflection of one of the outputted signals from a reflective object to determine the distance to the object. The apparatus has the function of determining a type of the object present in the object detectable zone. In the case where there are a plurality of signals produced by dispersion of a single shot of the laser pulse signals, and where distances derived by signals reflected from most of the object detectable zone show given shorter distance values, the object present in the object detectable zone is identified as a particle such as snow or fog floating in the air.
U.S. Pat. No. 4,699,507 (corresponding to Japanese patent application publication number 60-201276) discloses an apparatus and method for measuring the distance to a desired light-reflecting object. The apparatus and method in U.S. Pat. No. 4,699,507 are capable of recognizing erroneous measurements due to the presence of light-reflecting particles suspended in the air. The range of intensity of reflected light achievable by air-borne particles is previously stored. When the actual intensity of reflected light falls within the above-indicated range, the outputting of the measured distance to the light-reflecting object is inhibited.
U.S. Pat. No. 5,805,527 (corresponding to Japanese patent application publication number 9-236661) discloses a distance measuring apparatus which includes a wave transmitting device for emitting a transmission wave. The apparatus in U.S. Pat. No. 5,805,527 also includes a wave receiving device for receiving a reflection wave, which results from reflection of the transmission wave by a reflection object, as a reception wave. A time difference measuring device is operative for measuring a time difference between a moment at which the wave transmitting device emits the transmission wave and a moment at which the wave receiving device receives the reception wave. A distance calculating device is operative for calculating a distance to the reflection object on the basis of the time difference calculated by the time difference measuring device. An error correcting device is operative for detecting a time interval during which a signal level of the reception wave remains higher than a predetermined threshold level, and for correcting an error in the calculated distance to the reflection object on the basis of the detected time interval, the error being caused by a difference in intensity of the reception wave.
It is a first object of this invention to provide a method of accurately recognizing an object.
It is a second object of this invention to provide an apparatus for accurately recognizing an object.
It is a third object of this invention to provide a recording medium storing a computer program for accurately recognizing an object.
A first aspect of this invention provides a method of applying a transmission wave to a predetermined range in a width-wise direction of a subject vehicle, and recognizing objects located ahead of the subject vehicle on the basis of reflected waves which result from reflections of the transmission wave. The method comprises the steps of converting the reflected waves into a received signal; detecting a variation in an intensity of the received signal along a direction corresponding to the width-wise direction of the subject vehicle; separating the received signal into a first signal portion and a second signal portion on the basis of the detected signal intensity variation, the first signal portion corresponding to a scattered portion of the transmission wave, the second signal portion corresponding to an unscattered portion of the transmission wave; and recognizing objects on the basis of the second signal portion.
A second aspect of this invention provides an object recognition apparatus comprising radar means for applying a transmission wave to a predetermined range in a width-wise direction of a subject vehicle, converting reflected waves, which result from reflections of the transmission wave, into a received signal, and detecting objects on the basis of the received signal; and recognizing means for recognizing objects located ahead of the subject vehicle on the basis of results of detection by the radar means. The recognizing means comprises 1) means for detecting a variation in an intensity of the received signal along a direction corresponding to the width-wise direction of the subject vehicle; 2) means for separating the received signal into a first signal portion and a second signal portion on the basis of the detected signal intensity variation, the first signal portion corresponding to a scattered portion of the transmission wave, the second signal portion corresponding to an unscattered portion of the transmission wave; and 3) means for recognizing objects on the basis of the second signal portion.
A third aspect of this invention is based on the second aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises means for detecting the intensity of the received signal, and means for executing the separation of the received signal into the first signal portion and the second signal portion on the basis of the detected signal intensity.
A fourth aspect of this invention is based on the third aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises means for setting a threshold value equal to a peak value of the detected signal intensity minus a predetermined value, means for determining whether or not the detected intensity of the received signal is lower than the threshold value, and means for executing the separation of the received signal into the first signal portion and the second signal portion in response to a result of determining whether or not the detected intensity of the received signal is lower than the threshold value.
A fifth aspect of this invention is based on the second aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises means for calculating a rate of the detected signal intensity variation, and means for executing the separation of the received signal into the first signal portion and the second signal portion in response to the calculated intensity variation rate.
A sixth aspect of this invention is based on the fifth aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises means for setting a threshold value with respect to the calculated intensity variation rate corresponding to a predetermined steep state, means for determining whether or not the intensity of the received signal is lower than the threshold value, and means for executing the separation of the received signal into the first signal portion and the second signal portion in response to a result of determining whether or not the intensity of the received signal is lower than the threshold value.
A seventh aspect of this invention is based on the fifth aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises means for, when the calculated intensity variation rate corresponds to a predetermined gentle and monotonically-changing state, judging that a corresponding recognized object exists outside a predetermined recognition area.
An eighth aspect of this invention is based on the fifth aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises means for, when the calculated intensity variation rate corresponds to a predetermined gentle and monotonically-changing state occurring in a prescribed vehicle width-wise direction position, judging that a corresponding recognized object exists outside a predetermined recognition area.
A ninth aspect of this invention is based on the fifth aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises means for calculating a straight line approximate to the rate of the detected signal intensity variation in a least-squares method, means for calculating a slope of the straight line, and means for calculating the rate of the detected signal intensity variation from the calculated slope of the straight line.
A tenth aspect of this invention is based on the second aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises means for setting a threshold value with respect to the intensity of the received signal, means for using the threshold value in the separation of the received signal into the first signal portion and the second signal portion, and means for changing the threshold value on the basis of a size of a recognized object.
An eleventh aspect of this invention is based on the tenth aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises means for continuing the changing of the threshold value until a length of the recognized object in the width-wise direction of the subject vehicle falls into a predetermined range.
A twelfth aspect of this invention is based on the second aspect thereof, and provides an object recognition apparatus wherein the received signal contains a pulse, and a time difference between a leading edge and a trailing edge of the pulse increases as the intensity of the received signal rises, and wherein the recognizing means comprises means for estimating the intensity of the received signal on the basis of the time difference between the leading edge and the trailing edge of the pulse.
A thirteenth aspect of this invention is based on the second aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises condition estimating means for estimating whether or not there occurs a scatter condition that the transmission wave can be scattered, means for, only when the condition estimating means estimates that there occurs the scatter condition, executing the separation of the received signal into the first signal portion and the second signal portion.
A fourteenth aspect of this invention is based on the thirteenth aspect thereof, and provides an object recognition apparatus wherein the scatter condition comprises a condition that a waterdrop can meet a member of the radar means through which the transmission wave travels.
A fifteenth aspect of this invention is based on the fourteenth aspect thereof, and provides an object recognition apparatus wherein the condition estimating means comprises means for estimating whether or not there occurs the scatter condition on the basis of whether or not a windshield wiper of the subject vehicle is active.
A sixteenth aspect of this invention provides a recording medium storing a program for controlling a computer operating as the recognizing means in the object recognition apparatus of the second aspect of this invention.
A seventeenth aspect of this invention provides a method of applying a transmission wave to a predetermined range in a width-wise direction of a subject vehicle, and recognizing objects located ahead of the subject vehicle on the basis of reflected waves which result from reflections of the transmission wave. The method comprises the steps of converting the reflected waves into a received signal; wherein an intensity of a part of the transmission wave is maximized at a transmission center point, and is decreased as the part of the transmission wave becomes more distant from the transmission center point as viewed along the width-wise direction of the subject vehicle, and wherein a portion of the transmission wave which has an intensity equal to or higher than a prescribed intensity is effective for object recognition; detecting a rate of a variation in an intensity of the received signal along a direction corresponding to the width-wise direction of the subject vehicle; separating the received signal into a first signal portion and a second signal portion on the basis of the detected intensity variation rate, the first signal portion corresponding to the portion of the transmission wave which has the intensity equal to or higher than the prescribed intensity, the second signal portion corresponding to another portion of the transmission wave; and recognizing objects on the basis of the first signal portion.
An eighteenth aspect of this invention provides a method of applying a transmission wave to a predetermined range in a width-wise direction of a subject vehicle, and recognizing objects located ahead of the subject vehicle on the basis of reflected waves which result from reflections of the transmission wave. The method comprises the steps of converting the reflected waves into a received signal; wherein an intensity of a part of the transmission wave is maximized at a transmission center point, and is decreased as the part of the transmission wave becomes more distant from the transmission center point as viewed along the width-wise direction of the subject vehicle, and wherein a portion of the transmission wave which has an intensity equal to or higher than a prescribed intensity is effective for object recognition; setting a threshold value with respect to an intensity of the received signal; separating the received signal into a first signal portion and a second signal portion on the basis of the threshold value, the first signal portion corresponding to the portion of the transmission wave which has the intensity equal to or higher than the prescribed intensity, the second signal portion corresponding to another portion of the transmission wave; recognizing objects on the basis of the first signal portion; and changing the threshold value until a length of a recognized object in the width-wise direction of the subject vehicle falls into a predetermined range.
A nineteenth aspect of this invention provides an object recognition apparatus comprising radar means for applying a transmission wave to a predetermined range in a width-wise direction of a subject vehicle, converting reflected waves, which result from reflections of the transmission wave, into a received signal, and detecting objects on the basis of the received signal; and recognizing means for recognizing objects located ahead of the subject vehicle on the basis of results of detection by the radar means; wherein an intensity of a part of the transmission wave is maximized at a transmission center point, and is decreased as the part of the transmission wave becomes more distant from the transmission center point as viewed along the width-wise direction of the subject vehicle, and wherein a portion of the transmission wave which has an intensity equal to or higher than a prescribed intensity is effective for object recognition. The recognizing means comprises 1) means for detecting a rate of a variation in an intensity of the received signal along a direction corresponding to the width-wise direction of the subject vehicle; 2) means for separating the received signal into a first signal portion and a second signal portion on the basis of the detected intensity variation rate, the first signal portion corresponding to the portion of the transmission wave which has the intensity equal to or higher than the prescribed intensity, the second signal portion corresponding to another portion of the transmission wave; and 3) means for recognizing objects on the basis of the first signal portion.
A twentieth aspect of this invention is based on the nineteenth aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises means for setting a threshold value with respect to the calculated intensity variation rate corresponding to a predetermined steep state, means for determining whether or not the intensity of the received signal is lower than the threshold value, and means for executing the separation of the received signal into the first signal portion and the second signal portion in response to a result of determining whether or not the intensity of the received signal is lower than the threshold value.
A twenty-first aspect of this invention is based on the nineteenth aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises means for, when the calculated intensity variation rate corresponds to a predetermined gentle and monotonically-changing state, judging that a corresponding recognized object exists outside a predetermined recognition area.
A twenty-second aspect of this invention is based on the nineteenth aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises means for, when the calculated intensity variation rate corresponds to a predetermined gentle and monotonically-changing state occurring in a prescribed vehicle width-wise direction position, judging that a corresponding recognized object exists outside a predetermined recognition area.
A twenty-third aspect of this invention is based on the nineteenth aspect thereof, and provides an object recognition apparatus wherein the recognizing means comprises means for calculating a straight line approximate to the rate of the detected signal intensity variation in a least-squares method, means for calculating a slope of the straight line, and means for calculating the rate of the detected signal intensity variation from the calculated slope of the straight line.
A twenty-fourth aspect of this invention provides an object recognition apparatus comprising radar means for applying a transmission wave to a predetermined range in a width-wise direction of a subject vehicle, converting reflected waves, which result from reflections of the transmission wave, into a received signal, and detecting objects on the basis of the received signal; and recognizing means for recognizing objects located ahead of the subject vehicle on the basis of results of detection by the radar means; wherein an intensity of a part of the transmission wave is maximized at a transmission center point, and is decreased as the part of the transmission wave becomes more distant from the transmission center point as viewed along the width-wise direction of the subject vehicle, and wherein a portion of the transmission wave which has an intensity equal to or higher than a prescribed intensity is effective for object recognition. The recognizing means comprises 1) means for setting a threshold value with respect to an intensity of the received signal; 2) means for separating the received signal into a first signal portion and a second signal portion on the basis of the threshold value, the first signal portion corresponding to the portion of the transmission wave which has the intensity equal to or higher than the prescribed intensity, the second signal portion corresponding to another portion of the transmission wave; 3) means for recognizing objects on the basis of the first signal portion; and 4) means for changing the threshold value until a length of a recognized object in the width-wise direction of the subject vehicle falls into a predetermined range.